This invention relates to a method for reactivating a sulfonated resin catalyst for use in the polymerization of silicone oil, and more particularly, to a method for reactivating to a reusable level a sulfonated resin catalyst which has been used in the polymerization of silicone oil whereby the activity has been lowered due to adsorption of condensation water and clogging of micropores with gel and viscous materials.
Silicone oils are generally of a linear organosiloxane structure. Dimethylpolysiloxane oil on common use has a degree of polymerization of about 2 to about 2,100 and a viscosity of about 0.65 to about 1,000,000 centistokes (cs) at 25xc2x0 C. Silicone oils are produced by a variety of methods. In industrial plants, they are often produced by equilibration reaction of a raw material mixture containing a corresponding linear low molecular weight polymer, low molecular weight cyclics and end groups or a mixture of low and high molecular weight polymers in the presence of an acid or alkali catalyst. Typical silicone oils include dimethylsilicone oil of a dimethylpolysiloxane structure and methylphenylsilicone oil containing several to several ten moles of phenyl groups. They are widely used in the industry as heat resistant oil, cosmetic materials and parting agents.
In recent years, solid catalysts, especially solid acid catalysts become of interest from the standpoints of productivity improvement, product purity improvement and waste reduction, and have already been used.
Solid acid catalysts are used in several ways. In one exemplary way, the solid acid catalyst is set as a stationary phase in a continuous flowpath to enable a continuous production process, eliminating a catalyst removal procedure including neutralization, water washing and separation which is required in the prior art. In another simple way of usage, the solid acid catalyst is dispersed in a reaction solution by agitation, and after the completion of reaction, fractionated and removed using a screen or the like.
However, the solid acid catalysts reach the end of life due to a loss of catalysis over time, increased impurities in the product, an increased drive pressure through a continuous unit and the like, and are discarded after the expiration. It is desired to prolong the life of catalysts or to reactivate the used catalysts.
The method of producing silicone oil using solid acid catalysts is disclosed in JP-A 47-8646, JP-A 50-133299, JP-A 58-21427, etc. These patents describe nowhere the life of catalysts and the reactivation of used catalysts. In the literature, no reference has been made to the life of catalysts and the reactivation of used catalysts. These are technical problems to be solved before solid acid catalysts can be used in the industry.
An object of the present invention is to provide a method for reactivating a sulfonated resin catalyst for prolonging the catalyst life.
The inventors have found that a sulfonated resin catalyst which has been used in the polymerization of silicone oil whereby the activity has been lowered can be reactivated by washing the used catalyst (containing water) with a low molecular weight siloxane medium, volatilizing off the siloxane medium under atmospheric or reduced pressure, and removing water from the catalyst. With this method, the catalyst is effectively reactivated so that the service life thereof is prolonged.
One cause of catalyst deactivation is water. A trace amount of water is contained in the starting siloxane. Water forms through condensation of hydroxyl groups at ends of the starting low molecular weight siloxane polymer. It is believed that these water contents are adsorbed and deposited to surfaces of the catalyst and carrier resin. An attempt was made to dehydrate and dry the catalyst. However, the dehydrating/drying treatment alone was insufficient for complete reactivation of the catalyst.
Another cause of catalyst deactivation is thought to be the deposition of gel resulting from decomposition of siloxane organic groups by the strong acid catalyst and the deposition of foreign matter. An attempt was made to wash catalyst surfaces with a low molecular weight siloxane medium which is a low polymeric fraction of silicone oil. The washing alone failed to achieve complete reactivation of the catalyst, but when combined with the dehydrating/drying treatment, forwarded the catalyst reactivation to a reusable level.
Through these experiments, the inventors have found that a combination of low molecular weight siloxane medium washing with water removal, applied to a used solid acid catalyst, achieves a synergistic effect of reactivating the catalyst to an acceptable level.
Accordingly, the present invention provides a method for reactivating a sulfonated resin catalyst which has been used in the polymerization of silicone oil whereby the activity has been lowered, comprising the steps of washing the used catalyst with a low molecular weight siloxane medium, volatilizing off the siloxane medium under atmospheric or reduced pressure, and removing water from the catalyst.